The field of art to which this invention pertains is sterilization processes, in particular, ethylene oxide sterilization processes for medical devices manufactured from bioabsorbable polymers.
Ethylene oxide sterilization processes useful to sterilize medical devices manufactured from bioabsorbable polymers, such as absorbable surgical sutures, have long been known in this art. Examples of such processes are contained in U.S. Pat. Nos. 3,728,839, 3,815,315, 3,876,068, 5,287,634 and 5,464,580. The medical devices can be made from conventional, known bioabsorbable materials such as aliphatic polyesters, polylactides, polygycolides and polylactones and the like. In a typical ethylene oxide sterilization process for surgical sutures, packaged surgical sutures are typically placed in a specially configured sterilization chamber. A vacuum is then placed upon the chamber to remove residual air from the packages containing the sutures. Then, humidity in the form of steam or water vapor is transported into the sterilizer chamber in a sufficient quantity such that the water vapor permeates the suture packages and contacts the interior of the packages as well as the sutures. Next, ethylene oxide gas sterilant is charged into the sterilizer chamber and diffuses into the interiors of the packages and contacts the package interiors and the sutures. The ethylene oxide gas acts as a sterilant or sterilizing agent. It is known that ethylene oxide gas is highly flammable and explosive. Accordingly, sterilization processes have been developed wherein the ethylene oxide gas is mixed with non-reactive gases which acts as a diluent. Such gases include nitrogen, Freon(copyright) gas, and new environmentally friendly products, which replace the older chlorofluorohydrocarbons such as GENETRON(trademark) brand gas, which is a chlorofluorocarbon that is less likely to adversely affect the environment. The replacement of chlorofluorocarbons such as Freon(copyright) is desirable since it is believed that these compounds and entities may deplete ozone in the upper layers of the atmosphere.
Although the new diluent gases such as GENETRON(trademark) serve adequately as a component of an ethylene oxide sterilant gas, it is known that there are some problems associated with their use. In particular, it is believed that GENETRON(trademark) gas hydrogen bonds with plastics in packaging. This can be a problem particularly when degassing the sterilized medical device packages. The last stage of an ethylene oxide sterilization cycle is the degassing phase where it is necessary to degas or remove substantially all traces of the sterilant gas, diluent gas, sterilization by-products and moisture. Sterilization by-products in an ethylene oxide sterilization process are well known and include ethylene cholorhydrin, ethylene glycol, etc. This is accomplished by conventionally heating the interior of the sterilization chamber while pulling a vacuum on the sterilization chamber, or by placing the sterilized, packaged device into a separate degassing chamber and heating the interior of the chamber while pulling a vacuum. Heating the sutures in the chamber must be controlled to prevent possible degradation of the sutures. This may result in increased degassing times. Residual diluent gas in packaging materials may adversely affect seal integrity. Such a process is illustrated in FIG. 2.
What is needed in this art are new sterilization processes which can be used for the gas sterilization of bioabsorbable medical devices, such as absorbable sutures, which provide for the effective removal of sterilant gases, diluent gases, sterilization byproducts, and moisture without adversely affecting the packaging material or degrading the medical devices.
Accordingly, it is an object the present invention to provide a novel gas sterilization process useful with bioabsorbable medical devices, such as surgical sutures.
It is a further object of the present invention to provide such a process having improved efficiency while reducing the time needed to remove the residual sterilant gas, diluent gas, sterilization by-products and moistures during degassing cycles.
Therefore, a novel sterilization cycle is disclosed for gas sterilization of medical devices made from bioabsorbable medical devices. The process consists of initially providing a bioabsorbable medical device, such as a surgical suture, in a packaging pouch. Then, the medical device and pouch are placed in a chamber of a gas sterilant sterilizer. Next, a vacuum is pulled on the chamber and moisture is injected into the chamber. Then, a mixture of sterilant gas and an inert diluent is charged into the chamber and maintained for a sufficient time to effectively sterilize the device and the interior of the package. Then, the device and package are initially degassed by pulling a vacuum on the chamber, while increasing the temperature of the interior of the chamber to a first temperature and maintaining this temperature for a sufficient time to effectively remove substantially all of the moisture from the device and package. Finally, the device and package is degassed for a second time by pulling a vacuum on the chamber while increasing the temperature of the interior of the chamber to a second temperature , and maintaining that temperature for a sufficient time to effectively remove substantially all of the residual sterilant gas, diluent gas, sterilization by-products, and moisture from the device and package without degrading the bioabsorbable medical device.
These and other advantages and aspects of the present invention will become more apparent from the following description and accompanying drawings.